Method for injection molding a parison



Sept'. l, 1970 E. l. wml 3,526,681

METHOD FOR INJECTION MOLDING A PARISON original Filed April 25. 196s 2Sheets-Sheet 1 Sept. 1970 E. l. VALYI METHOD FOR INJECTION MOLDING -APARISON Original Filed April 25,1966

FiG. 3

2 Sheets-Sheet 3 INVENToR. Eme/U I \/^L"/ United States Patent 3,526,687METHOD FOR INJECTION MOLDING A PARISON Emery I. Valyi, 5200 SycamoreAve.,

Riverdale, Bronx, N.Y. 10471 Division of application Ser. No. 544,898,Apr. 25, 1966,

now Patent No. 3,387,324, dated June 11, 1968, which is acontinuation-impart of applications Ser. No.

326,410, Nov. 27, 1963, and Ser. No. 353,004, Mar. 8,

1964. This application Aug. 28, 1967, Ser. No. 675,725

Int. Cl. B29c 17/07; B29d 23/02 U.S. Cl. 264--97 1 Claim ABSTRACT F THEDISCLOSURE A method for injection molding a parison to be subsequentlyblow molded. A two part blow core having a blow port which is closableby relative movement of the two parts is positioned within an outerparison die member having side and end walls shaped to form the side andend walls of the parison. Holding pressure is exerted on one of theparts to cause the core to seat against the end wall of the parison diemember and to close the blow port. Plastic is injected through a passagein the outer die member to form the side walls of the parison while thecore remains seated against the end wall of the outer die. The injectionof plastic is continued while the holding pressure on the core isreduced so as to allow the core to retract a distance necessary to formthe bottom wall of the parison, the blow port being maintained closed bythe pressure of the injected plastic. The finished parison with the coreis removed from the outer die and placed in a blow mold where the blowport is opened and blowing air introduced therethrough in order to formthe parison against the blow mold.

This application is a division of my copending application Ser. No.544,898 tiled Apr. 25, 1966, now Pat. No. 3,387,324 dated lune 1l, 1968,which is a continuationin-part of applications Ser. No. 326,41-0 tiledNov. 27, 1963 now abandoned, and Ser. No. 353,004 led Mar. 8, 1964, nowabandoned.

This invention relates to a method for blowing hollow articles from aparison and more particularly to a method for making a parison oforganic plastic material and expanding the same in a blow mold.

An object of the invention is to provide novel and improved method ofthe above type.

Various other objects and advantages will be apparent as the nature ofthe invention is more fully disclosed.

In accordance with the present invention, the parison is molded on atwo-piece blow core which is initially seated against the bottom of theparison die for centering the vblow core While the side walls of theparison are being injected. After the side walls have been formed, theblow core is retracted by the pressure of the injected plastic materiala sutncient distance to provide a clearance for forming at least a partof the bottom of the parison. During this entire injection period, theblow ports in the blow core are held closed by the holding pressurewhich is exerted on the blow core to oppose the pressure of the plasticmaterial and to hold the core seated. The blow ports are opened onlyafter the blow core with the parison thereon has been introduced intothe blow mold and is in position for blowing.

The nature of the invention will be better understood from the followingdescription, taken in connection with the accompanying -drawings inwhich a specific embodiment has been shown for purposes of illustration.

In the drawings:

FIG. 1 is a longitudinal section with parts in elevation of a parisondie showing the blow core seated against the bottom of the outer diemember and the plastic injected to form the side walls of the parison;

IFIG. 2 is a similar view showing the blow core retracted to form thebottom wall of the parison; and

FIG. 3 is a similar view showing the blow core in blow position withinthe blow mold and the hollow article in the blow mold cavity.

Referring to the drawings more in detail, the invention is shown asembodied in a blow molding apparatus comprising an outer parison diemember having split side walls 10 and a bottom wall 11y shaped toconform to the outer surfaces of the parison walls to be formed therein.The bottom wall 1'1 includes a sprue having a central passage 12 for thehot atiowable plastic and communicating with a series of radiallyextending passages 13 terminating in a ring of injection openingsdisposed to inject the plastic into the side walls of the parison.

The central passage 12 communicates with an injection chamber 2.2through a slide valve 15 actuated by a piston 16 working in a iluidcylinder 17 the fluid pressure to which is controlled by a solenoidvalve 18 which is adapted to open and close the valve 15 in response toa feeler Contact to be actuated by retraction of the blow core.

The plastic material is supplied to the chamber 22 through passage y14having a check valve 23. Pressure is exerted in chamber 22 by a ram 24causing the plastic material to flow through passage 12 while valve 15is open and check valve 23 is closed.

The blow core 30 comprises a lower portion 31 having side walls 32 and abottom wall 33 adapted to deiine the inner surfaces of the correspondingparts of the parison walls. The bottom wall 33 is adapted to seatagainst the bottom wall 11 of the outer parison die member for centeringthe blow core in the parison die while the side walls of the parison arebeing injected.

The other blow core part comprises a -slidable member 35 having anoutside diameter which is the same as or larger than that of the blowcore walls 32. The slidable member 35 is disposed to slide over a stem36 of the blow core and to engage a yshoulder 37 on the blow core toform a continuous outer surface around which the parison is formed. Theblow core stem 36 is provided with an axial passage 38 for blow airterminating in radial ports 40 adjacent the shoulder 37. The slidablemember .35 is shown in the form of a sleeve which extends past the end41 of the stem 36 and has a closure member 42 forming a uid cylinder 43into which uid under pressure may be supplied through an inlet passage44 and in which the end 41 of the stem 36 slides. The arrange- `ment issuch that uid pressure in the cylinder 43 causes relative movement ofthe slidable member 35 and the blow core part 31 for opening the blowair ports 40 and thereafter the fluid pressure is supplied through theblow air ports from the cylinder 43 through the passage 38 and the ports40 for blowing the parison.

An O-ring 45 carried by the slidable member 35 engages the stem 36 ofthe blow core part 31 to exert friction for preventing relative movementof the slidable member and core when the slidab-le member and stem arebeing retracted from ythe parison die. Alternatively, a tension springmay be introduced into the cylinder 43 to hold the slidable member inengagement with the shoulder 37 in absence of uid pressure in thecylinder 43. The end 41 of the stem 36 may be formed with a shoulder 46engaging a shoulder 47 on the slidable member to form a stop to limitthe sliding movement of the stem 36 in the slidable member 35 when thecylinder 43 is pressurized.

The closure member 42 carries a head 51 forming a piston sliding in acylinder 52 formed in a cross-head 53. Hydraulic pressure is supplied tothe cylinder 52 through Patented Sept. 1, 1970 a passage SS which may beclosed by a valve 56. An adjustable stop 57 limits the retraction of thehead 51 of the rod 50 into the cylinder 52 and a shoulder 58 limits theextension of the head 51 so that the entire blow core is retracted withthe cross-head 53 when the latter is raised. The crosshead 53 isactuated by a hydraulic cylinder 59 for shifting the blow core betweeninjection and blowing positions.

The blow mold is shown in FIG. 3 as formed in two parts 60 and 61 havinga cavity 62 therein shaped to form the hollow article. A neck ring 53 isdisposed to form the neck of the parison and to hold the neck inposition during the blowing of the hollow article.

In the operation of this apparatus, the cross-head 53 is advanced toseat the bottom wall 33 of the blow core against the bottom wall 11 ofthe outer die member as shown in FIG. 1. The cross-head cylinder 52 islled with hydraulic Huid through the passage 55 under a pressure toadvance the head 51 to seat the blow core 31 on the bottom wall 11 ofthe parison die, and the valve 56 is then closed to maintain the head inthis position. The cross-head 53 and slidable member 35 then move as aunit and carry the blow core part 31 which has been extended by airpressure in the cylinder 43 during the previous blowing operation sothat the blow ports 40 are o en.

pWhen the bottom wall 33 of the blow core seats against the bottom wall11 of the lower die member, continued advance of the cross-head 53causes the slidable member 35 to advance with respect to the blow corepart 31 until it engages the shoulder 37 to close the blow ports 40 andto form a continuous surface for the parison Wall cavity. The valve 15is then opened and hot ilowable plastic material is injected to formside walls 70 of the parison as shown in FIG. l.

At a selected time during the injection of the side walls, the valve 56is opened to release the hydraulic pressure in the cross-head cylinder52. When the pressure of the plastic on the bottom wall 33 of the blowcore becomes rsufficiently high to overcome the hydraulic pressure inthe cross-hea-d cylinder, the blow core 30 is retracted against the stop57 which -is set -to provide clearance between the bottom of the blowcore and the bottom of the outer die member for forming at least aportion of the bottom wall of the parison. The bottom wall 71 is theninjected as shown in FIG. 2 to complete the parison. During this entiretime the slidable member 35 is held against the shoulder 37 by thepressure of the plastic against the bottom wall 33 so that the blowports 40 remain closed.

After the parison has set to the proper point, the outer die members areopened slightly to free the outer surface of the parison walls 70 andthe blow core, with the parison thereon, is retracted from the injectionposition into blow position by suitable actuation of the crosshead 53.

When in blow position, the blow mold parts 60 and 61 are closed aroundthe parison and air pressure is supplied to the cylinder 43 to causerelative movement of the slidable member 35 and blow core part 31 toopen the blow ports 40 and to supply air through the blow ports toexpand the parison into the blow mold cavity 62 as shown in FIG. 3 andthus form the hollow article 72.

After the article has been blown, the blow core is retracted by furthermovement of the cross-head 53, the blow mold opened and the finishedarticle removed. The blow core is then returned into the injection dieand the cycle repeated.

4 -In this apparatus it is to be noted that the blow ports Vin the blowcore are automatically opened and closed by the movement of thecross-head which transfers the blow core between injection and blowpositions and by the blow air which is supplied at the blow position.Also the blow core is centered by the seating of the bottom wall of theblow core and then retracted by the pressure of the plastic after theside walls have been formed.

When the head 51 has been retracted in the cylinder 52 against the stopS7, it engages a plunger 74 which in turn actuates a switch which isconnected to energize the solenoid 18 so as to close the valve 15 andinterrupt the injection of the plastic before the parison die is opened.Alternatively, a pressure actuated switch may be connected to be closedin response to the pressure of the plastic material which would becomegreater when the parison cavity is filled. In either case, the pressureof the plastic in the injection passage is released before the parisondie is opened.

What is claimed is:

1. The method of injection molding a parison of flowable organic plasticmaterial on a two part blow core having a blow port which is closable byrelative movement of the two parts, in an outer parison die memberhaving side and end wall-s shaped to form the side and end walls of theparison, and blowing the parison in a blow mold having a cavity shapedto form the blown article which comprises introducing the blow core intothe parison die while exerting holding pressure on one of said parts tocause said blow core to seat against the end wall of said outer parisondie member and to close said blow port, injecting the plastic through apassage in the outer die member to form the side walls of the parisonwith the blow core seated aga-inst the end wall of the outer die member,reducing the holding pressure and continuing the injection of theplastic under a pressure adapted to retract said blow core by a distanceto provide clearance for the formation of at least a part of the endwall of the parison and to maintain said blow port closed and continuingthe injection of the plastic to complete the formation of said end wall,incorporating said blow core with the parison thereon in the blow mold,separating the parts of said blow core to open said blow port andexpanding said parison into conformity with the blow mold cavity byfluid pressure introduced through said blow port.

References Cited UNITED STATES PATENTS 2,453,739 11/ 1948 Bates 264--328X 2,825,093 3/1958` High. |3,238,287 3/ 1966 Chapman 264-278 X 3,301,9281/1967 'Plymale 18-581 X 3,314,105 4/ 1967l Amsden. 3,339,231 9/ 1967Piotrowski.

FOREIGN PATENTS 909,555 10/ 1962 Great Britain. 962,726 6/ 1950 France.

ROBERT F. WHITE, Primary Examiner J. H. SILBAUGH, Assistant ExaminerU.s. C1. XR. 264-328, 18-5

